What does the Fixed Frame mean in rviz?

answered 2014-11-19 07:42:06 -0500

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updated 2018-02-19 07:49:29 -0500

It's the tf frame that all positions/measurements that you see are relative to. For example, let's say you have a robot that has two frames, odom (a world-fixed frame) and base_link (the body frame of the robot). The robot is at position (10, 0) with a heading of pi/2 in the odom frame, and it has a LIDAR on board that sees an obstacle 5 meters directly in front of it. If you set your Fixed Frame to odom, that obstacle will appear at position (10, 5). If you set your Fixed Frame to base_link, it will appear at (5, 0).

EDIT: updating answer for comment from @malharjajoo

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Thank you so much.

Does the Grid always be the world coordinate? If I set /odom as the fixed frame. Rviz will draw obstacle at potions (10, 5) in the Grid?

I think the heading in your assumption should be pi/2.

somebodyus ( 2014-11-19 08:01:15 -0500 )edit

Yeah, fixed that, sorry. Need coffee.

And yes, if you set the fixed frame to /odom, the obstacle will be drawn at (10, 5).

Tom Moore ( 2014-11-19 08:11:31 -0500 )edit

@tom, I didn;t really follow your explanation, what does heading = pi/2 mean ( is the robot facing left by 90 degree compared to lidar) ?

also could you elaborate how the (10,0) and (10,5) works out ? can't seem to visualize that based on the explanation.

malharjajoo ( 2018-02-07 16:55:00 -0500 )edit

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